This chart posted at io9 exposes the many liberties filmmakers take with science in movies about space. The only two films to receive a clean bill are true stories from history. Link -via The High Definite

Apollo 13 was great, and almost perfect, but there was one thing that bugged me every time I saw it. The gauge showing CO2 percentage should have been moving very slowly, but every time they showed it the hand was sweeping dramatically towards the danger point. It would have been fatal in seconds if it continued moving at that speed, and each time they showed it it started from the same lower point and swept up. Should have been still in the shots, each time at a slightly higher level.

All planets have Earth gravity. No, they all had earth-like gravity. Endor's was a little lower, Hoth's a little higher. All planets have a climate planet-wide. Alderaan, Endor, Yavin, and Naboo had multiple climates. Bespin and Hoth might well have had a gradient of gas giant and snow world climates respectively. Coruscant would have before it became an unending city with climate control.Easy communication with aliens. Protocol droids and 25,000 years of interspecies interaction.Nearby asteroids aren't drawn close by gravity. We saw asteroids for minutes and they were moving at unrealistically high speeds and close to each other. This one is not really able to be ruled on without at least a few hours of star wars asteroid footage.Faster-than-light travel. Hyperspace is like sub-space, you don't move faster than light, you shift into a plane where the relative distances are warped shorter and traverse them at sub-light speeds. That's why you use the sublight engines in hyperspace.

Enemy Mine:

All planets have Earth gravity. Two planets are shown with two earth-like gravities.All planets have a climate planet-wide. Two planets with variable climates and seasons.Easy communication with aliens. Two aliens in the entire galaxy that have had a prolonged war, probably have special teams dedicated to translating war messages and codes, and it takes a long time for them to learn each others' language.